1. Technical Field
The present invention relates to a power converter, and in particular, to a power converter that determines a current command according to an output voltage and uses, as bases, the current command and an input current to generate a drive signal for driving a switching element.
2. Related Art
A power converter is well known, which determines a current command according to an output voltage and uses, as bases, the current command and an input current to generate a drive signal for driving a switching element. For example, JP-A-2006-033958 discloses a switching regulator as such a power converter.
This switching regulator includes an oscillator, an error amplifier, a comparator a RS flip-flop, and a switch. The oscillator outputs a set signal at every predetermined cycle. The error amplifier generates and outputs a current command based on a reference voltage, which corresponds to an output voltage command, and an output voltage. Specifically, the error amplifier obtains a difference between the reference voltage and the output voltage and outputs the difference as a current command. The comparator generates and outputs a reset signal based on the current command, which is outputted from the error amplifier, and an input current. Specifically, the comparator outputs a reset signal when an input current reaches a current instructed by the current command. The RS flip-flop generates and outputs a drive signal. The drive signal is turned on in synchronization with the set signal to turn on the switch. Also, the drive signal is turned off in synchronization with the reset signal received thereafter to turn off the switch. The switch is turned on/off according to the drive signals. Thus, the input voltage is converted to the voltage instructed by the output voltage command and the converted voltage is outputted.
In the switching regulator set forth above, if the error amplifier or the comparator has a failure or a malfunction, the reset signal is no longer outputted correctly. When a reset signal is not timely outputted, the switch is not timely turned off to allow the on-state to continue. Thus, the switch is overheated, due to overcurrent and breaks down.
Further, in the switching regulator set forth above, when the input voltage is increased, the output voltage is also increased accordingly. When the output voltage is increased, the error amplifier, the comparator and the RS flip-flop will adjust the drive signal so that the output voltage is suppressed from being increased. Therefore, even when the input voltage is increased, the increase in the output voltage is suppressed.
However, the error amplifier, the comparator and the RS flip-flop have their respective response delays. These response delays are accumulated before the drive signal is generated. Moreover, the input voltage is not taken into account in generating the drive signal. Therefore, when the input voltage is rapidly increased, the drive signal cannot be immediately adjusted in response to the drastic increase. In this case, the output voltage is inevitably increased.